The　reasonable　establishment　of　rotor　dynamics　model　is　very　important　in　the　study.　This　paper　establishes　a　dynamic　model　of　the　rotor,　and　gets　the　numerical　calculation　of　the　frequencies　and　mode　shapes　of　the　rotor　under　the　free　condition.　The　modal　of　the　rotor　bearing　system　is　analyzed　by　using　software.　Compared　to　the　above　two　kinds　of　results,　the　test　of　turbocharger　rotor　mechanics　correctly　modeled　is　to　prove　that　this　method　has　practical　significance.